In order to fully understand the fundamental concepts in biology it is necessary to have a strong grasp on evolution and the mechanisms of evolution. Arguably the most important of these mechanisms, and quite likely also the most difficult to understand, is natural selection. When Charles Darwin published his definitive text- On the Origin of Species by Means of Natural Selection -it caused a revolution in the scientific world and ultimately shaped our understanding of the Life Sciences. It is for these reasons that I decided to focus only on natural selection in this presentation on the mechanisms of evolution.
Natural Selection
Curriculum Connection-SBI3U
Specific Expectations:
C2.4 investigate, through a case study or computer simulation, the processes of natural selection and artificial selection (e.g., selective breeding, antibiotic resistance in microorganisms), and analyse the different mechanisms by which they occur [PR, AI, C]
C3.4 describe some evolutionary mechanisms (e.g., natural selection, artificial selection, sexual selection, genetic variation, genetic drift, biotechnology), and explain how they affect the evolutionary development and extinction of various species (e.g., Darwin’s finches, giraffes, pandas)
Natural Selection - what students need to understand:
1. More offspring are produced than can survive in a population due to limited resources. Individuals within a population have variable traits that are heritable.
2. Some heritable traits are advantageous to an individual and by having these traits they are more likely to survive and reproduce thereby passing these traits to their offspring. Heritable traits are the only traits affected by natural selection.
3. Natural selection operates at the individual level, but only populations evolve. Populations change over time as the number of individuals with advantageous traits for their environment increases.
4. A population evolves to the environment in which it lives. If the environment changes the gene pool of the population will change as different traits will confer advantage in different environments.
Required Background Knowledge
A very basic knowledge of genetics is necessary prior to understanding natural selection. A student should know (at the very least) that:
genes are inherited (passed from parent to offspring)
some traits are a result of the genetic make-up of an individual
The internet is filled with excellent resources to help you develop the background knowledge needed to teach this topic. This video is one example and provides an excellent explanation of natural selection using examples from a hummingbird population in Ecuador. The Teachers Resources section contains many other similar resources.
Student Misconceptions
Below are some misconceptions and that students may about natural selection. This list was modified from a more extensive list of misconceptions about all areas of evolution which may be found at: Understanding Evolution
Natural selection involves organisms trying to adapt. Actually: Natural selection is a random process acting on the genetic variation of individuals within a species. The organisms are not "trying" to adapt. Some organisms have traits that are better suited to their environment allowing them to produce more offspring than other organisms of their species.
Natural selection gives organisms what they need and acts for the good of the species. Actually: There is no intent involved in natural selection so the needs of an organisms are not a factor in the process. Natural selection is a RANDOM process that results in changes within a species over generations.
The fittest organisms in a species are those that are strongest, healthiest, and/or largest. Actually: An organisms fitness is determined based on its ability to contribute genetic material to the species. This is accomplished by producing offspring that are also able to contribute genetic material to the species. An organism that is able to produce more offspring than others in the species is considered to be more fit.
Natural selection produces organisms perfectly suited to their environment. Actually: Natural selection is an ongoing process that results in observable changes over generations of a species. There is no intent in natural selection to create the perfect organism; a species adapts over time as a result of environmental pressures.
Societal Issues
Opponents of Evolution
The theory of evolution is still an issue of debate in many school boards within American States. Fortunately, our Ontario curriculum requires us to teach evolution and its mechanisms as we would any other scientific principle. However, this does not mean that you will not encounter students or parents who "do not believe in evolution". This can lead to a difficult situation as some people believe that the theory of evolution conflicts with their religious beliefs. How can we resolve this conflict without offending the beliefs of our students or their parents?
As teachers in Ontario our mandate is to teach the curriculum provided to us by the Ministry. You may want to begin a conversation by advising parents that it is not our choice but rather our duty to teach this theory. This approach may help to remove any feeling that you are personally attacking anyone's beliefs. Each situation will require a unique resolution but for each it is important to be sensitive to the beliefs of our students while maintaining the standards set out by the Ministry documents.
To further address this issue you may wish to begin a discussion with any person opposed to the teaching of evolution about the idea that both ideas are valid and do not necessarily negate each other. An interesting essay (and subsequently a book) was published by the late great evolutionary biologist Stephen Jay Gould reflecting on this issue. In his book Rock of Ages-Science and Religion in the Fullness of Life, Dr. Gould explores an idea he titles non-overlapping magesteria (NOMA) wherein the theory of evolution in no way conflicts with a belief in religion. He submits that the teaching of religion is confined to the subjects of moral meaning and value and the teaching of science is for the purpose of exploring the empirical universe. The subjects are governed by two separate majesteria which do not overlap, hence the name non-overlapping magesteria (NOMA). If you are curious to explore this theory further a link to the essay is posted below. NOMA essay
GMOs
Genetically Modified Organisms or GMOs are a topic of controversy lately as these products have found their way onto the shelves of our supermarkets. Through genetic modification and artificial selection scientists have been able to manufacture crops resistant to drought, viruses, and pests. They are able to produce increased crop yields with higher nutrition levels. But many people question the long term effects of these GMOs on human health and the environment. This issue would make a great classroom debate topic.
Hook
After students have been introduced to the basic idea of evolution, have them examine the two skulls seen in the pictures below. Ask them to provide an explanation about how the species of skull #1 evolved to become the species of skull #2? You may ask them to describe what was happening in the environment? What other changes were happening at the population level, etc.?
Students will have an understanding that species evolve through time, but this activity will start them thinking about the processes that drive this evolution.
Skull 1
Skull 2
Pairs to Squares
This activity would be useful after students have been introduced to the concept of natural selection (after one or two lessons).
1. Have students find a partner.
2. Assign each group a number, either 1 or 2.
3. Ask the students of group 1 to create a hypothetical animal population with at least three variable heritable traits. Have the students write out a description of their animals including the variable heritable traits, what the animals eat, where they live, and how they reproduce. They will create images of their animals so that others can envision what they are describing.
4. Ask the students of group 2 to create a hypothetical environment. Have them write a description about their environment including the temperature, the seasons, the plants that grow there, what animals might live there, etc. Have them illustrate their environment so that others can quickly envision what they have described.
5. Have pairs form squares composed of one group 1 and one group 2. Each group will explain what they have created.
6. Ask students to choose which of the traits will be advantageous in the environment and which will act as a disadvantage and explain their choices in a group report.
7. Have pairs present their findings to the class.
8 Ask students to predict what will happen to the animal population after several generations in an individual journal entry
This file provides instructions to create a board game type activity to illustrate natural selection
from http://www.explorebiology.com
Another link to a virtual lab which explores the increase of favourable mutations and the decrease of unfavourable mutations in a population. There are also many more virtual labs for all science subjects found at this site.
This is a complete teaching module for natural selection. It addresses the barriers to understanding this concept, includes a diagnostic test, lab activities, problem sets, and other great material. If you are going to teach evolution this is a must read!
Taken from http://education.msu.edu/irt/PDFs/OccasionalPapers/op091.pdf
This is a link to great information about teaching natural selection. It includes the necessary background information as well as detailing student misconceptions and how to address them. The site was developed by the University of California Museum of Paleontology.
This link will take to to a site hosted by San Diego State University with resources for teaching biology concepts. Concept cartoons can be found here which are useful for introducing conflict into students pre-conceptions about a concept. SDSU Biology Teaching Page
These are journal articles regarding student misconceptions in understanding natural selection.
Mechanisms of Evolution
In order to fully understand the fundamental concepts in biology it is necessary to have a strong grasp on evolution and the mechanisms of evolution. Arguably the most important of these mechanisms, and quite likely also the most difficult to understand, is natural selection. When Charles Darwin published his definitive text- On the Origin of Species by Means of Natural Selection -it caused a revolution in the scientific world and ultimately shaped our understanding of the Life Sciences. It is for these reasons that I decided to focus only on natural selection in this presentation on the mechanisms of evolution.
Natural Selection
Curriculum Connection-SBI3U
Specific Expectations:
C2.4 investigate, through a case study or computer simulation, the processes of natural selection and artificial selection (e.g., selective breeding, antibiotic resistance in microorganisms), and analyse the different mechanisms by which they occur [PR, AI, C]
C3.4 describe some evolutionary mechanisms (e.g., natural selection, artificial selection, sexual selection, genetic variation, genetic drift, biotechnology), and explain how they affect the evolutionary development and extinction of various species (e.g., Darwin’s finches, giraffes, pandas)
Natural Selection - what students need to understand:1. More offspring are produced than can survive in a population due to limited resources. Individuals within a population have variable traits that are heritable.
2. Some heritable traits are advantageous to an individual and by having these traits they are more likely to survive and reproduce thereby passing these traits to their offspring. Heritable traits are the only traits affected by natural selection.
3. Natural selection operates at the individual level, but only populations evolve. Populations change over time as the number of individuals with advantageous traits for their environment increases.
4. A population evolves to the environment in which it lives. If the environment changes the gene pool of the population will change as different traits will confer advantage in different environments.
Required Background Knowledge
A very basic knowledge of genetics is necessary prior to understanding natural selection. A student should know (at the very least) that:
The internet is filled with excellent resources to help you develop the background knowledge needed to teach this topic. This video is one example and provides an excellent explanation of natural selection using examples from a hummingbird population in Ecuador. The Teachers Resources section contains many other similar resources.
Student Misconceptions
Below are some misconceptions and that students may about natural selection. This list was modified from a more extensive list of misconceptions about all areas of evolution which may be found at:
Understanding Evolution
Societal Issues
Opponents of EvolutionThe theory of evolution is still an issue of debate in many school boards within American States. Fortunately, our Ontario curriculum requires us to teach evolution and its mechanisms as we would any other scientific principle. However, this does not mean that you will not encounter students or parents who "do not believe in evolution". This can lead to a difficult situation as some people believe that the theory of evolution conflicts with their religious beliefs. How can we resolve this conflict without offending the beliefs of our students or their parents?
As teachers in Ontario our mandate is to teach the curriculum provided to us by the Ministry. You may want to begin a conversation by advising parents that it is not our choice but rather our duty to teach this theory. This approach may help to remove any feeling that you are personally attacking anyone's beliefs. Each situation will require a unique resolution but for each it is important to be sensitive to the beliefs of our students while maintaining the standards set out by the Ministry documents.
To further address this issue you may wish to begin a discussion with any person opposed to the teaching of evolution about the idea that both ideas are valid and do not necessarily negate each other. An interesting essay (and subsequently a book) was published by the late great evolutionary biologist Stephen Jay Gould reflecting on this issue. In his book Rock of Ages-Science and Religion in the Fullness of Life, Dr. Gould explores an idea he titles non-overlapping magesteria (NOMA) wherein the theory of evolution in no way conflicts with a belief in religion. He submits that the teaching of religion is confined to the subjects of moral meaning and value and the teaching of science is for the purpose of exploring the empirical universe. The subjects are governed by two separate majesteria which do not overlap, hence the name non-overlapping magesteria (NOMA). If you are curious to explore this theory further a link to the essay is posted below.
NOMA essay
GMOs
Genetically Modified Organisms or GMOs are a topic of controversy lately as these products have found their way onto the shelves of our supermarkets. Through genetic modification and artificial selection scientists have been able to manufacture crops resistant to drought, viruses, and pests. They are able to produce increased crop yields with higher nutrition levels. But many people question the long term effects of these GMOs on human health and the environment. This issue would make a great classroom debate topic.
NatureEducation examines GMOs
Student Activities
HookAfter students have been introduced to the basic idea of evolution, have them examine the two skulls seen in the pictures below. Ask them to provide an explanation about how the species of skull #1 evolved to become the species of skull #2? You may ask them to describe what was happening in the environment? What other changes were happening at the population level, etc.?
Students will have an understanding that species evolve through time, but this activity will start them thinking about the processes that drive this evolution.
Pairs to Squares
This activity would be useful after students have been introduced to the concept of natural selection (after one or two lessons).
1. Have students find a partner.
2. Assign each group a number, either 1 or 2.
3. Ask the students of group 1 to create a hypothetical animal population with at least three variable heritable traits. Have the students write out a description of their animals including the variable heritable traits, what the animals eat, where they live, and how they reproduce. They will create images of their animals so that others can envision what they are describing.
4. Ask the students of group 2 to create a hypothetical environment. Have them write a description about their environment including the temperature, the seasons, the plants that grow there, what animals might live there, etc. Have them illustrate their environment so that others can quickly envision what they have described.
5. Have pairs form squares composed of one group 1 and one group 2. Each group will explain what they have created.
6. Ask students to choose which of the traits will be advantageous in the environment and which will act as a disadvantage and explain their choices in a group report.
7. Have pairs present their findings to the class.
8 Ask students to predict what will happen to the animal population after several generations in an individual journal entry
This file provides instructions to create a board game type activity to illustrate natural selection
from http://www.explorebiology.com
This is a link to a virtual lab and the accompanying worksheet
Virtual Lab-Natural Selection
Another link to a virtual lab which explores the increase of favourable mutations and the decrease of unfavourable mutations in a population. There are also many more virtual labs for all science subjects found at this site.
Conflicting Selection Pressures
Teaching Resources
This link will take you to my concept presentation.Prezi-Mechanisms of Evolution
This is a complete teaching module for natural selection. It addresses the barriers to understanding this concept, includes a diagnostic test, lab activities, problem sets, and other great material. If you are going to teach evolution this is a must read!
Taken from
http://education.msu.edu/irt/PDFs/OccasionalPapers/op091.pdf
This is a link to great information about teaching natural selection. It includes the necessary background information as well as detailing student misconceptions and how to address them. The site was developed by the University of California Museum of Paleontology.
Understaing Evolution
This link will take to to a site hosted by San Diego State University with resources for teaching biology concepts. Concept cartoons can be found here which are useful for introducing conflict into students pre-conceptions about a concept.
SDSU Biology Teaching Page
These are journal articles regarding student misconceptions in understanding natural selection.
For those who wish to dig a little deeper, here is a link to an online version of the original Darwin text.
On the Origin of Species by Means of Natural Selection